The present invention relates to an arrangement for displacing a roll, which is hydrostatically journalled by its axle on support structures and positionable in its working position by means of a bearing, through a rapid movement of the bearing out of its said working position, said journalling comprising at each end of the roll at least one loading element pressurizable with a hydraulic medium and at least one support element. The invention is particularly suitable for the quick release of a roll nip constituted by two rolls, but it is by no means intended to be limited to just this particular application.
The quick release of a roll nip is required for example with calenders using coated soft-surface rolls in the event of a web break for avoiding roll surface damages. Heretofore, the quick release of a roll nip has been effected by means of external loading cylinders by releasing from the cylinders a holding pressure which supports the bottom roll. In such a traditional design, the nip force progresses along a long route through the lower cylinders and the entire frame structure from bottom roll to top roll. The lower cylinders necessitate a set of valves and often the use of a separate individual aggregate. The Applicant""s earlier Finnish patent application 970625 discloses a control system for the bearings of a hydrostatically journalled roll, which enables the execution of a quick action for the roll by means of the journalling. As a result of carrying out the quick release of a roll nip by means of a lower cylinder bearing, the lower cylinders included in the traditional design can be omitted and, if necessary, the configuration of calenders can be modified in such a way that the rolls are linked directly to each other by means of coupling elements present at the ends of the rolls. Thus, the coupling element transmits the nip force and the machine frame structures can be lightened and the loading system strengthened by virtue of a shorter transmission chain. The elimination of lower cylinders also results in a simpler control system.
One object of the present invention is to provide an improved arrangement for effecting a rapid movement for a hydrostatically journalled roll by means of a bearing. In order to achieve this objective, an arrangement of the invention is characterized in that the arrangement comprises a valve control piston, delivering a hydraulic medium required for the pressurization of said at least one loading element and positioned in a valve cylinder, said control piston being provided with a positioning valve on the face of the control piston pointing towards the loading element, the face of the control piston opposite relative to the positioning valve being coupled with a pressure line of the hydraulic system for focusing a holding pressure on the control piston.
A In another preferred embodiment of the invention, the arrangement further comprises a quick-action piston for effecting the rapid movement, positioned in a quick-action cylinder, one face of said piston being coupled with a pressure line for focusing a holding pressure on the piston, the opposite face of said piston being coupled with a quick-action pressure line extending to a pressurization side of said at least one loading element, and that, in order to effect a rapid movement of the bearing, the quick-action cylinder is adapted to remove a constant volume of hydraulic medium consistent with a desired rapid movement range from the pressurization side of said at least one loading element, while a holding pressure in the pressure line acting on said pistons has been released.
In yet another preferred embodiment of the invention, the pressure line for the valve cylinder and the quick-action cylinder is provided, in connection with each cylinder, with a holding valve which is adapted to open as a result of releasing the supply pressure of the pressure line, said opening of the holding valve releasing said holding pressure of the pistons.
The arrangement of the invention is suitable for use in a nip constituted by a deflection-compensated self-loading type roll and a counter roll provided with a stroke-effecting slide bearing of the invention.